This invention relates generally to a zoom lens, and more particularly to a zoom lens system designed for use on video cameras.
In recent years video cameras have decreased in size and weight and, with this, zoom lenses for use on them are now required to decrease in size and weight as well. On the other hand, these zoom lenses are required to have a higher zoom ratio and be made wider-angle (i.e., to have a shorter focal length and hence a field covering a wider angle). It is thus now demanded to achieve such high performance simultaneously with the achievement of size and weight reductions.
For instance, JP-A 4-296809 discloses one typical zoom lens for video cameras, and states that such a zoom lens, albeit small, can achieve a high zoom ratio, and a shorter focal length and hence a field covering a wider angle. The disclosed zoom lens is of a zoom type wherein all lens groups are movable along the optical axis during zooming.
Of zoom lenses for a silver salt type of photographic cameras, on the other hand, a zoom lens of the type that all lens units are movable for zooming is set forth in JP-A 57-5012 for instance.
The former conventional zoom lens has a zoom ratio as high as about 12, but is inadequate in terms of the half field angle at the wide-angle end, as can be seen from .omega.=31.5.degree., and the latter one has an enough half field angle at the wide-angle end, as can be seen from .omega.=37.degree., but has a zoom ratio of about 3 that is insufficient for use on a video camera.